Seeing what's there: Is your fuel contaminated?

It can be easy to miss subtle, or even large amounts of fuel contamination. Can you spot slight differences in fuel quality?

If aircraft ran on water, the aviation industry would look very different, indeed. But aircraft exhibit a distinctly negative reaction to being fueled with water, dirt, or anything other than fuel--which is why a thorough fuel inspection upon each refueling is essential. Even trace amounts of something that isn’t fuel can cause mechanical damage, malfunctioning parts, and forced landings. Though it’s a concern that may be scoffed at by some, accidents are still occurring due to fuel contamination, making it worth a reexamination.

A closer look

When inspecting fuel, you’re on the lookout for three primary categories of impurity: water, particulates, and microbial growth. We’ll touch on water in a moment, but particulates and microbial growth are often the easiest to spot--though they can still be deceptive.

Particulates can be anything from dirt to rag pieces to bugs to dust, and tend to settle in fuel tanks. When sampling, swirling the fuel to create a vortex will isolate particulates.

Microbial growth is actually a sign that your fuel is also contaminated with water, as it occurs when bacteria in water make contact with fuel. The result is a sludge-like substance that can cause internal troubles such as corrosion and blocked filters.

Wait about half an hour after an aircraft has been fueled before sampling, then ensure you’re examining the sample in a well-lit area. Hold the fuel up to the light. If you see anything at all in the fuel that appears suspect, off-colored, or a different texture than the fuel, treat it as you would a contaminated sample.

Searching for water

You’re probably already aware of how water looks when mixed with fuel--it sinks to the bottom, and won’t mix with the fuel at all. Though it can be a bit more difficult to detect in small amounts, you’ve trained yourself to look closely at the bottom of the container, right?

But have you considered cases where the fuel is extremely contaminated--so much so, that there is far more water than fuel? In these cases, small bubbles of fuel will lightly color the water to give it the appearance of the fuel, but without a clear line between the two, you may not notice that you just poured yourself a glass of water rather than fuel. This is especially dangerous with light-colored fuels.

A good way to detect water in any amount is to add a few drops of food coloring to the liquid. The coloring will mix well with water, highlighting its presence, but will avoid fuel and settle in the bottom of the container if no water is present.

Water enters a fuel system in two ways: through an improperly sealed fuel cap, causing rain, water from washing, or other sources to flow inside, or through condensation within the tank that occurs slowly, over time. Double check your fuel cap every time it’s been removed and never fail to check the fuel for water or contaminants that can enter through other means.